History of the AtomTimeline Project

Jessica Coniglio

Democritus 460 BC• Democritus proposed an

Atomic Theory which states that all atoms are small, hard indivisible and indestructible particles. It also states that these particles are made of a single material formed into different shapes and sizes.

http://reich-chemistry.wikispaces.com/Jette+.Ancient+Times+(450+ADand+years+prior)

Dalton 1803• Dalton's experiments on gases led to

his discovery that the total pressure of a mixture of gases amounted to the sum of the partial pressures that each individual gas exerted while occupying the same space. In 1803 this scientific principle officially came to be known as Dalton's Law of Partial Pressures. Dalton's Law primarily applies to ideal gases rather than real gases, due to the elasticity and low particle volume of molecules in ideal gases. http://

www.biography.com/people/john-dalton-9265201

Mendeleev1869

• Mendeleev created the first valid periodic table of the elements in 1869. He created a table of the known elements (63 at the time) in ascending order by atomic weight, grouped together by similarities in properties.

http://webpub.allegheny.edu/employee/g/grodgers/ScientificTravelingWebsite/Mendeleev.html

Eugene Goldstein 1885• In an experiment in

1886, Goldstein punctured the anode and observed glowing yellow streamers coming from the punctures. He termed them Kanalstrahlen or canal rays.http://

www.xtimeline.com/evt/view.aspx?id=629217

Henri Becquerel1896• Becquerel became one of the many scientists fascinated

by Wilhelm Röntgen's discovery of x-rays. He Wondered if the "penetrating rays" were related to the luminescence he had studied for years. He experimented with a sample of potassium uranyl sulfate crystal and a photographic plate. Exposing the sample to sunlight, he placed the crystal in a darkroom next to the photographic plate. Though the plate showed developed streaks, indicating the presence of penetratingrays, he noticed the effect whether the crystal had been exposed to light ornot. This eliminated the possibility of a luminescent connection, and Becquerel realized he had discovered a new type of penetrating ray. Further researchshowed that only crystals that contained uranium would develop the plate, and that a disk of pure uranium metal produced penetrating rays nearly four times as intense as his original sample.Becquerel presented his findings to the world in May of 1896, labeling thesenew emissions Becquerel rays. http://biography4u.com/marie-curie-

radioactivity.html

J.J. Thomson 1897• J.J. Thomson achieved the original

study of cathode rays culminating in the discovery of the electro which was announced to the Royal Institution on April 30th, 1897. Thomson theorized that the rays were streams of small subatomic particles. He called them "corpuscles," which meant "small bodies” in Latin. He figured his negatively charged “corpuscles” accounted for about one-thousandth of the mass of a hydrogen atom, matched by a positive charge elsewhere in the atom. In 1897 he later theorized that the negative electrons swarmed around in a "sphere of uniform positive electrification.”

http://www.nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-bio.html

Ernest Rutherford 1907• In 1907 Rutherford, along with

Thomas Royds, carried out a chemical test that involved allowing of alpha rays to penetrate a very thin window into an evacuated tube. The rays always sparked the tube into discharge resulting in a spectrum that changed its nature as the alpha rays accumulated in the tube. Further into the experiment it showed how the clear spectrum of helium gas started to appear. This went on to prove that alphas were in the minimum possibilities ionised helium atoms or probably helium nuclei.

http://www.thefamouspeople.com/profiles/ernest-rutherford-140.php

Millikan 1910• Millikan made numerous

momentous discoveries, mainly in the fields of electricity, optics, and molecular physics. His earliest major success was the accurate determination of the charge carried by an electron, using the elegant "falling-drop method”.http://www.nobelprize.org/

nobel_prizes/physics/laureates/1923/millikan-bio.html

Frederick Soddy1913• In 1913 he formulated the

concept of “radio elements chemically non-seperable”. Dr Margaret Todd suggested to name them “isotopes”.

http://www.universitystory.gla.ac.uk/biography/?id=WH0182&type=P

Neils Bohr1913• In 1913 Bohr published a classic

paper, On the Constitution of Atoms and Molecules. He was awarded the Nobel Prize in 1922 due to the recognition of his work on the structure of atoms .

http://www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html

Heisenberg1925• In 1925 Heisenberg

proposed a new formula in the fields of physics. His first important paper work on the particulars of quantum mechanics was published in 1925 and the formula of the "uncertainty principle" came out in 1927http://myarticle-

article.blogspot.com/2012/07/biography-of-werner-heisenberg.html

Chadwick 1932• Chadwick helped answer Physicists question

when identifying the neutron (particle without an electric charge in the nucleus) in 1932. Chadwick had created an experiment to answer the question of this unknown nucleus mass source. He smashed alpha particles into beryllium and allowed the radiation that was released to hit another target (paraffin wax). When the beryllium radiation hit hydrogen atoms in the wax, the atoms were sent into a detecting chamber. In physics it is known that only a particle having almost the same mass as a hydrogen atom could effect hydrogen in that manner. The experiment results showed a collision with beryllium atoms would release massive neutral particles, which Chadwick named neutrons. This provided the answer for hidden mass in atoms. Chadwick's discovery advanced experimental work for all scientists.

http://www.light-science.com/chadwick.html

Works cited1. http://www.nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-bio.html2. http://www.wired.com/science/discoveries/news/2008/04/dayintech_04303. http://www.thefamouspeople.com/profiles/ernest-rutherford-140.php4. http://myarticle-article.blogspot.com/2012/07/biography-of-werner-heisenberg.html5. http://www.biography.com/people/john-dalton-92652016. http://www.nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.html7. http://www.sciencewithmrjones.com/downloads/chemistry/scientists/history_of_the

_atom_-_scientists_-_resource_sheet.pdf

8. http://www.faqs.org/health/bios/22/Antoine-Henri-Becquerel.html9. http://www.light-science.com/chadwick.html10. http://www.universitystory.gla.ac.uk/biography/?id=WH0182&type=P11. http://www.who2.com/bio/dmitri-mendeleev12. http://

www.cartage.org.lb/en/themes/Biographies/MainBiographies/G/Goldstein/1.html